Effect of water potential and temperature on growth sporulation and production of micro sclerotia by verticillium dahliae
Ioannou, N.; Schneider, R.W.; Grogan, R.G.; Duniway, J.M.
Phytopathology 67(5): 637-644
The minimum osmotic potential (.psi.s) which allowed conidial germination, mycelial growth and sporulation of V. dahliae was -100 to -120 bars. Radial growth on agar medium was maximal at .psi.s values between -10 and -20 bars, but growth measured as increase in dry weight decreased linearly with decreased .psi.s of liquid medium from -2 to -120 bars. Likewise, the rate and final percentage of conidial germination decreased progressively with each decrease in .psi.s below -2 bars. The production of conidia in liquid medium logarithmically as .psi.s decreased from -2 to about -20 bars and was maximal at .psi.s values as low as -50 bars. No (or very few) microsclerotia (MS) were produced at .psi.s values between -70 and -80 bars, even though radial growth and production of dry weight were reduced by only 60% at these same .psi.s values. The production of MS either was increased or remained unchanged by reduction of .psi.s from -2 to about -20 bars and it decreased progressively with greater reductions in .psi.s. The production of MS in infected tomato stems buried in nonsterilized soil was maximal at a water potential (.psi.) of -32 bars and at 24.degree. C. Appreciable numbers of MS also were produced at 18, 27 and 30.degree. C in soil at .psi. = 5 or -32 bars. However, in saturated soil and soil at .psi. = -100 bars the production of MS was greatly inhibited at all temperatures tested. When infected stems were adjusted by air-drying to .psi. values ranging from -5.8 to -98 bars and buried in soil at .psi. = -27.5 bars and 24.degree. C, maximal numbers of MS were produced in tissue dried to .psi. = -18.7 bars. When similar tissues were buried in soil at .psi. = -0.8 bars only small numbers of MS were produced, regardless of the initial water status of the tissues.